Surface modified Mg-doped ZnO QDs for biological imaging

Abstract

Nanocrystals of ZnO are currently attracting great interest as potential labels for biological applications, such as theranostic devices, due to their luminescent properties and low toxicity in vivo. It has been reported that doping with Mg 2+ ions could enhance the luminescence of ZnO quantum dots (QDs). In the present study Mg-doped ZnO QDs were synthesized by a hydrolysis and condensation reaction. Surface modification of the QDs was performed using oleic acid (OA) to hinder their aggregation and to provide them colloidal stability in non-polar environments. Mg 2+ ions could be incorporated into the ZnO wurtzite lattice owing to the very close values of the Mg 2+ and Zn 2+ ion radii. However, the dopant ions strongly influenced the growth and final size of ZnO nanocrystals, as evidenced by time-resolved synchrotron SAXS measurements. The presence of Mg prevented the aggregation of the primary nanoparticles. Doping with Mg 2+ ions widened the band gap of ZnO QDs and enhanced their visible luminescence. With increasing proportion of Mg 2+ ions, both the absorption and emission spectra experienced a blue shift. The luminescence went through a maximum for a 20 mol% nominal concentration of Mg 2+ ions in the reaction medium. The quantum yield (QY) of 20 mol% Mg-doped ZnO colloidal suspension (64%) was about 6 times higher than that of the ZnO suspension (10%). Mg-doped ZnO QDs capped by OA formed stable colloidal dispersions in chloroforme, with strong visible fluorescence (QY = 38%), promising for biological imaging.

Surface modification of ZnO quantum dots by organosilanes and oleic acid with enhanced luminescence for potential biological application

“…QY results showed that the surface modifiers do not interfere significantly when compared to the ZnO-QDs colloidal suspension (10.2%), which corroborated with the QY reported by Manaia et al [36]. The results related with ZnO-QDs capped by GPTMS and HTMS can be explained by reduction of defects present in the crystal structure (as seen above).…”

“…The lower photoluminescence intensity in the yellow spectral range for bare ZnO-QDs probably occurred during acquisition of the ZnO-QDs in powder form. The above results are different from that found for the ZnO-QDs colloidal suspension prepared by sol-gel route, which having shown a great photoluminescence in the green spectral range [36]. This phenomenon might be related with the security of NPs in function of colloidal protection, which is lost after the ZnO-QDs powder obtaining.…”

ZnO Nanostructures for Drug Delivery and Theranostic Applications

“…Moreover, the luminescence of ZnO nanocrystals can be improved or modulated by doping the structure with other ions [ 9 , 10 ].…”

The Critical Role of Thioacetamide Concentration in the Formation of ZnO/ZnS Heterostructures by Sol-Gel Process

“…They are used in a wide range of applications such as photocatalysts, sensors, electroluminescent devices and lasers [ 1 , 2 , 3 , 4 ]. More specifically, ZnO quantum dots (QDs) are promising luminescent probes for bioimaging due to their biodegradability and very low toxicity in vivo [ 5 , 6 , 7 , 8 , 9 ]. In recent years, ZnO/ZnS heterostructures have emerged as an attractive approach for tailoring the particle characteristics and properties [ 10 , 11 ].…”